Introduction: 12 Volt DC Solar Power Supply
Finalist in the
Off the Grid Contest
Here I will show you how I used Recycled lawn/garden solar lights to make a 12 volt power supply/charger.
I think I have about $8.00 in it so far!
Step 1: What the End Result Looks Like
Okay lets get started.
I when on to a recycle website and asked for used garden solar lights, working or not.
After getting a response I went and picked up about 15 of these from a very nice person. Some lights worked about 1/2 did not. Mostly this was poor care.
These solar lights were of a higher price/quality type. You will notice each cell is upside down and has a switch to allow the LED to turn on or not. I'm pretty sure this is for storage.
I put the lights in the off position and left them off. For this project you will not need the lights and the solar cells will continue to charge the batteries.
I found the case I am using for this project at Harbor Freight for about $5-6 on sale.
Step 2: Dis-assembly of the Garden Lights
Sadly I did not take pictures of this part as I had not intended to make an instructable out of this project.
These cells were out of lights that were round on top. the Metal peice forms a frame around the square cell. You will find that often the cells are held in place on the underside by Silicon caulk/adhesive. An exacto or box knife will cut through some of this and allow with CARE the cells to be removed.
********** CAUTION Knives are sharp and should be handled with care!!!!!! I found that by going slow and careful I was able to salvage every cell and my hand as well.
You can see how I placed all the cells for soldering.
The cells are wired in Series / Parallel configuration. So in essense 6 cells with batteries are wired + to - in a row. Mind you I had to place the 6th cell on each string in the upper part of the box so as to make it all fit.
There are 2 rows of 6 cells in series basically side by side... these rows are connected + to + on one end of the strings and - t - on the other. this becomes like on big battery.
You can see the series connection if you look for the U SHAPE Black and Red wires bridging between cells. One row is Black the other Red.
Step 3: A Bit About Rechargeable AA Batteries.
In the last step you saw the rechargeable AA batteries.
AA rechargeables are only 1.2 volts when charged, not 1.5 like a standard Alkaline battery out of the pack.
You will notice there are a variety of batteries in this array.
I had to make due with the batteries I could find that would still work and hold some charge. So far so good, but time will tell after a few charges.
So if you look there are 2 cells on each solar fixture. You can tell that 2.4 volts will be all it can produce when charged.
2.4 volts x 6 solar fixtures = 14.4 volts.
This is enough voltage to regulate, and run 12 volt DC items. ***** MOST not all 12 items can take a supply voltage of up to 13.8 volts with out damage.
***** A general rule of thumb, if your appliance can plug into a car cigarette lighter there is a good chance it can take 13.8 volts.
In the box you will see a blue surface that the cells rest on. This is 1/2 inch carpet padding. I needed a way to keep them from sliding all over and to also not damage the LED assemblies should I ever want to use the lights for some purpose.
Under the padding layer I took and old (CLEAN) hand/dish towel and folded it. I needed just a bit more thickness but not another 1/2 inch of padding.
Bingo it worked.
Step 4: What Is the Output Voltage, Lid Open With No Load Applied
As you can see the DVM reads 14.96 volts.
Most solar cells produce enough power with no load to really suprise you. once regulated or a load is applied the voltage drops.
The call for current (amps) causes a voltage sag. We still want a voltage great enough to charge the cells beneath them.
As a side note I had a 13 watt CFL bulb on over the work space while testing the cells.
Remember we have two series strings each producing 14.96 volts DC. When wired in parallel we didn't raise the voltage but rather doubled the current/amperage potential. THUS we should see less of a voltage sag when a load is applied.
Now let us close the cover!
Step 5: What Is the Output Lid Closed With No Load Applied
Now with the cover closed you see a charge voltage drop of .08 not much at all. The somewhat opaque lid does filter a bit of the light energy.
I had thought the difference would be much higher than it actually was.
Now we need to see about a 1 volt of drop in order to reach a normal charge voltage for a 12 volt battery. (13.8 volts)
Most car alternators produce about 13.8 volts with the use of a regulator to prevent over charging.
I have not pictured it here but there are two ways to help regulate this charger/supply.
If you are just going to use this pack to power say a small CB/Ham radio, one that can take a few amps of current I would suggest using one or two zener diodes to cause the voltage to drop.
Most zener diodes will drop a voltage aprox 1/2 to 1 volt when placed in series with the load. You will have to test one then two and find out what works for your situation. I would also suggest the use of a fuse in line with the load.
For this pack I would use 1-3 amp fuse, most likely a 2 amp if I could find one.
Step 6: What I Used
As you know from previous steps I used a very inexpensive digital volt meter. I found mine for about $6 at a local ham radio fest several years back.
I also used 18 gauge (AWG) < American Wire Gauge size hook up wire.
This wire was fairly flexible. Stranded wire is best. It is so much easier to use and also less likely to break when bent to the shapes you will need for this type of project.
You can also see the paste flux and thin flux core solder.
Most people make the mistake of thinking you can solder with just the rosin/flux in the solder. I'm sorry but you will be pulling your hair out!!!!!!!!!!!!!
If your solder surface is not clean/free of debris you will not get a good molecular bond in the solder joint.
If bare metal is not covered by flux while soldering <<<(especially for a beginner) you will find the solder will ball up and not flow.
What is happening here is this :
The metal to be soldered WITH OUT FLUX oxidizes to quickly under heat that no solder can bond.
The name of the game is keep the joint clean until the solder flows!!!!!!!! ALWAYS!!!!!!
By lightly coating the wires/joint to be soldered with paste flux the joint will stay clean while hot. You pretty much assure that this will be a good joint.
A moist OLD sponge ( would you would use just for soldering or throw away afterwards) is good to help keep the solder iron tip clean. Keep the sponge MOIST don't totally wring it out.
Often you can lightly dip the hot iron in the paste flux. It will smoke a bit. Then wipe the tip on the sponge. DO NOT BURN YOURSELF!!!! after you see the iron come shiny clean, apply some fresh solder to the tip. << This is called tinning the tip!
****** REMEMBER ******* where you put the heat from the tip is where the solder will be apt to flow. If you can hold the tip under the joint you will have a more uniform connection <<< HEAT RISES thus a more even heat on the joint.
I may do a video on soldering at some later date.
Soldering is not really as hard as it appears, you just have to mind the laws of physics.
ABOUT THIN SOLDER!!! : Unless you are going to sweat copper pipe or make some very large joint DO NOT USE THICK SOLDER!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
the Thins solder serves several key purposes in easy soldering. The first being with thin solder you can see what is happening at the joint. Second thin solder will melt faster and can be feed at your speed instead of waiting for thicker solder to melt, drip or be so long melting that the joint oxidised or worse yet burn up. THIS IS SO important when soldering small , thin wire connections.
Soldering around components like resistors, capacitors, diodes requires a good in and quick out strategy.
Keep the moist sponge handy you may want to touch the joint quickly after releasing the iron in order to cool a component and save its tiny life :) SMILE!
ALSO thin solder allows you to keep feeding the solder until the joint looks to have enough solder. Often people do not use enough solder and the joint is weak. If you have the luxury of not soldering near components. make sure you get a good flow with the iron. Get the iron out and let the joint sit for about 3-4 seconds before blowing on it or using a sponge.
This allows the solder to set/cool a bit. This way when you touch it with a sponge the joint sets up harder since the molecules are closer together and do not freeze mid point by immediate cooling, creating a weak/brittle joint.
Step 7: THE END !!!
Basically this is what you get. I am fortunate to have a balcony on my apartment. unfortunately the parking lot light is attached right next to the balcony so it never gets dark there even at night.
SO IF YOU ARE GIVEN LEMONS MAKE LEMONADE!!
I chose to use the light to charge my solar pack. I set the pack on the balcony rail ( 3rd floor )and allowed it to charge.
OH if you decide to regulate the voltage of this supply, you can also use 78XX series regulator like a 7812 or you can use an LM317
which will allow you almost total control over the voltage regardless if you want to lower the voltage to 13.8 or down to 9,6,5 or what ever volt you chose.
***** REMEMBER with a regulator the wider the span between the original voltage and the end voltage the more wasted power you will have. I.E. 14.4 volts and say 3 volt out. What a waste truely!
If you google LM317 you can download a data sheet for it. Bing also has some images of circuit options. The Android market has a program FREE called electrodroid.
This program had within it a LM317 calculator built in. You enter the input voltage and the output voltage and it draws the schematic along with part values. EASY!!!!! for you newbies..
Radio Shack, Ebay, and other supply houses like Jameco have these parts, they are NOT expensive!
Good Luck! If you have questions ask away!
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Please be positive and constructive.